Chemical dyes are important compounds for a range of applications. For example, inkjet inks typically comprise at least one colorant in the form of a dye. Many dyes are charged molecules carrying either a positive or negative charge, which is balanced with a counterion. The present invention specifically relates to cationic salts of sulfonated dyes.
In the field of inkjet inks, it is important for any colorant to be stable over a prolonged period of time (e.g. at least 5 years, at least 10 years or at least 20 years). For example, it is desirable that photos printed from an inkjet printer do not fade significantly over time. Generally, it is desirable for inkjet-printed photos to behave comparably to traditional photos.
Inkjet colorants printed onto a surface may degrade via a number of mechanisms. In particular, poor stability in the presence of ozone and other atmospheric oxidants is a major drawback of many potential viable dyes. As used herein, the resistance of a dye to ozone and other atmospheric oxidants is referred to as “ozonefastness”.
Some attempts to minimize the sensitivity of dyes to ozone have been made in the prior art. For example, the introduction of an impermeable barrier between the dye and the atmosphere improves the lifetime of the dye by physically limiting its exposure to ozone. Typically, this is achieved by lamination of printed material or by encapsulation of the dye molecule.
Another means for improving the lifetime of a dye is through the use of ozone scavengers, such as electron-rich olefins. Ozone scavengers may be formulated with the dye, chemically bonded to the dye or incorporated into print media so as to improve the lifetime of the dye.
IR absorbing dyes are particularly susceptible to ozone degradation. IR dyes are useful in printing inks, such as inkjet and offset inks. The present Applicant has been concerned with the development of an IR ink for use in its Netpage and Hyperlabel™ systems, which are described extensively in the cross-referenced patent applications herein.
The Netpage and Hyperlabel™ systems generally require a substrate having a coding pattern printed thereon. The coding pattern is preferably printed with an IR-absorbing ink having minimal visibility, so that it does not interfere with the visible content of the substrate. A user can interact with the substrate using an optical sensing device, which reads part of the coding pattern and generates interaction data. This interaction data is transmitted to a computer system, which uses the data to determine what action is being requested by the user. For example, a user may make handwritten input onto a form, click on a printed hyperlink, or request information relating to a product item. This input is interpreted by the computer system with reference to a page description corresponding to the printed substrate.
It is desirable for printed netpages to allow user interactions over prolonged periods of time so that they may, for example, be archived and retain their interactivity. It is therefore desirable that IR inks, used to print the coding pattern, have excellent stability and are not degraded by ozone and other atmospheric oxidants.
Likewise, it is desirable that other inks (e.g. CMYK inks) have excellent stability and are not degraded by ozone and other atmospheric oxidants.